1. Field of the Invention
The present invention relates to a printing system including a printing machine using a transfer belt for transferring a sheet to make a print thereon.
2. Description of Related Art
There have been known printing systems including a printing machine adapted to transfer a sheet as a print medium held on a transfer belt and to make a print thereon by propelling droplets of ink from an ink head onto the sheet.
When such a printing system is put in a printing service, the transfer belt is driven in a controlled manner for a constant travel speed. However, the travel speed of the transfer belt may change by so-called irregularities in thickness of the transfer belt in addition to similar affection by eccentricity of rollers over which the belt is stretched.
The transfer belt may thus travel at non-constant speeds causing droplets of ink propelled out of the ink head to be shot in positions deviated from desirable positions on a sheet, i.e. subject to so-called “shot deviations”. Shot deviations debase the print quality of printed images.
To suppress such shot deviations, there has been a technique disclosed in a patent literature 1 (WO 2009/113597). This technique includes operations for storage of belt profile data representative of irregularities in thickness of a transfer belt and roller profile data representative of eccentricity of rollers over which the transfer belt is stretched, as they are extracted in advance. Then, it operates for use of a combination of belt profile data and roller profile data to control ink discharge timings, to suppress shot deviations.
The above-noted technique involves the use of an encoder detecting roller revolutions to measure a travel speed of the transfer belt every pulse outputted from the encoder in order to generate a belt profile data and a roller profile data. Then it employs data of such measurements to calculate therefrom an average travel speed for use to determine a speed ratio of a measured travel speed to the calculated average travel speed for each pulse.
A set of the determined speed ratios is employed as a data set constituting a basis for calculations to determine a set of fractions therein attributable to eccentricity of associated rollers, to provide the above-noted roller profile data. The data set of speed ratio is then processed to remove therefrom the set of fractions attributable to roller eccentricity, to provide the above-noted belt profile data.